{"html":"<!DOCTYPE html>\n<html>\n\n<head>\n <meta charset=\"UTF-8\">\n <style>\n \n div{\n position: relative/* 确保伪元素可以相对于div定位 */\n }\n\n div::after{\n content:\"\";/*内容*/\n display: block;/*伪元素能够按照块级元素进行显示*/\n width: 20px;\n height: 20px;\n background-color: rgb(255,0,0);\n }\n \n </style>\n</head>\n\n<body>\n <div></div>\n <script type=\"text/javascript\">\n // 填写JavaScript\n </script>\n</body>\n\n</html>","css":"","js":""}